Control device



March 14, 1939. Tl s SAFFOD 2,150,403

CONTROL DEVICE Filed Deo. 28, 1954 2 Sheets-Sheet l INVENTOR TRUM/l/V 5. .SAF/:0199

March 14, 1939. T. s' SFFQRD v 2,150,403

I CONTROL DEVICE 2 Sheets-Sheet 2 Filed Dec. 28, 1934 INVENTOR 72H/mq 534/- 0 a. ATTORNEY;

Patented Mar. 14, 1939 PATENT OFFICE 2,150,403 CONTROL DEVICE Truman S. Sanford, Riverside, Conn. Application December 28, 1934, Serial No. '159,455

15 Claims.

This invention relates to a device for automatically regulating the operation of refrigera` tion apparatus so as to prevent the excessive accumulation of frost deposits thereon. More par- 5 ticularly the invention relates to 'thermostatic devices responsive to conditions of frosting and e. The problem of defrosting refrigerators is one which has received a great 1o and, especially in the use of household refrigerators, it has become common practice to provide a convenient switch for interrupting the operation of the refrigerating device `so as to permit the melting of accumulated frost. Cer- 15tain devices for this purpose have been widely advertised as automatic defrosters", but in fact are automatic only in so far asttheyrestore the normal operation of the device after the defrosting is complete. Certain devices have also been 9,0 suggested for a tomatically initiating defrosting,

but these have not been adopted, and it has comsupposed that fully automatic demonly been frosting was impracticable because it is highly objectionable to have the defrosting period occur g5' at a time when rapid. freezing of ice cubes of desserts is desired.

In my prior application Serial No.'618,220, filed June 20, 1932, I have disclosed la fully automatic defrosting device which is designed to 'avoid any 3o interference withthe use of the refrigerator.

- The objects of my present invention are similar to those of my said prior application, and I have now found that these`obiectsk may be attained l within the broad scope of, vbut in ways and by 35 devices superior in any respects to those speci- 1 cally disclosed in my prior application.

The present application is a continuation in part of my said prior application and I am claiming herein the broad invention of which different 40 s peciflc embodiments are disclosed in this and my said prior. application.

In the accompanying drawings I have shown a preferred embodiment of my invention and a number of modifications thereof. These draw- 45 ings are not intended to be exhaustive and are not to be taken as limiting of the invention, but on the contrary, are chosen with a view to illustrating my invention and explaining the principles involved therein so that others skilled in the ,-,0 art may apply it under varying conditions of practical use and may make such modificationsand changes therein as such conditions may make desirable.

Tn these drawings I have shown in:

55 Figure '1, in vertical section, of a domestic redeal of attention;

' vthey may be separate.

, frigerator with the cooling unit and thermostatic devices diagrammatically represented to'indicate the position of these units in the preferred embodiment of my invention.

Figure 2, a diagram of the circuit by which the 5 refrigeration is controlled in' the preferred embodiment of my invention.

Figure 3, in axial section.- another type of thermostatic circuitl controlling device which l, may be substituted for the particular type shown in the other figures.

vFigure 4, in elevation, another type of circuit controlling device.

Figure 5, a diagram of another embodiment of my invention. l5

Figure 6, in elevation, a modification in which two thermostats are mechanically instead of eleo. trically interconnected.

Figures '7 and 8, side views respectively of the two thermostats shown in Figure 6.

Figure 9, a diagram of another embodiment which employs a. snap thermostat switch on one side with the thermostat and electrical relay on the other side.

Figure 10, a diagrammatic view of another embodiment dening a snap thermostat switch with a mechanical delay device.

Figure l1, an end view of the electrical connection for the mechanical delay of Figure l0.

Figure 12, a view similar to Figure 11 showing 30 a modified delay device, and j 'Figures 13 and 14, a modied thermostatic circuit control showing respectively the o and on positions.

Fig. 15 -is a fragmentary sectional viewtaken 35 `on line Iii- I5 of Fig. l.

Referring first to Figure 1, it may be stated generally that my invention contemplates the use of a thermostat positioned within the freezing ice cubes, desserts, etc., in household refrigerattemperature frozen liquids will terminate defrosting. andsecondly, the provision of a device which is responsive to a decrease in thermal Jconductivity of the cooling surfaces which device shall automatically initiate defrosting. In some cases the two devices may be identified, whereas in other cases Ordinarily,` however, for sakeof economy vit is desirable that both functions should be performedby the same thermostatic devices. i In Figure l, I have shown diagrammatically the to serve these functions. At I0, I have indicated but sensitive to the the box of a domestic refrigerator; at II,'the door by which access is had to the interior of the box; at I2, the cooling unit or evaporator; at I3, a thermostatic device outside of the evaporator,

thereby, and at I4, by a broken line I have indicated a. thermostatic device on the interior of the chamber within the cooling unit and positioned so as to be sensitive tothe temperature of liquids whichmay be placed therein for freezing, and to the temperature of the atmosphere in said chamber, but preferably insulated from direct heat-exchanging with the cooling surfaces of the chamber. Thus it may be just above the ice trays, or in a recess in a shelf on which such `tray is heldor atthe end of the ice tray space in close association'with the ends of the trays.

'Ihese thermostats, I3 and I4, may be of various typeaand in the drawings I have shown several types merely for `the purpose of illustration, understanding of course that the choice may be from numerous others upon considerations well understood-1n the art.

In Figure,l I havel illustrated diagrannnatically g the thermostats I3 and I4 as bi-metallic spiral therefrom so as to strips each adapted to engage respectively the IS-IG and I-l-IB of the tilting switches I9 and 20, e. g., mercury switches.

These switches, I9 and 20, are, as shown in Figure 2,.connected in series with each other and with the motor 2I from the power line 22.

vhlach switch is balanced so that it will stay in either position to which it is moved. The flow of mercury'to one side or the other of the pi'vot serving to hold it tilted. y

The thermostat I3 is adapted to move the finger I5 when the upper temperature limit of the range permitted within the box I0 adjacent the cooling unit I2 has been attained, and to move the fingers I6 to tilt the switch in the opposite direction when the lower'limit of that range is attained. In order that this thermostat may serve to maintain a more or less constant temperature in the atmosphere throughout .the box and not be too sensitive to the operation of the cooling unit, the thermostat I3 should be placed at a'substantial distance from the cooling surface or shielded be effected more by convection than by direct radiation.

The thermostat I4 is set so'that, at a temperature below that ordinarily attained in the freezin g chamber when the cooling unit is free from frost, it contacts and moves the -flnger I8 to open the switch 20, whereas at a temperature which is on the outside of the cooling surfaces.

indicative of the presence of unfrozen liquids within the chamber, or of completion of defrosting, it will contact and move the linger I'l to the closed circuit position.

In the operation of this device we may assume by way of example that a temperature is to be maintained at the thermostat I3 between the range ofl 40 and 50 F. and that in the normal operation of the refrigerating device, the interior of the freezing chamber at the thermostat I4 will not drop below F. We may assume-a temperature of F. as one indicative of unfrozen liquids. This temperature is also chosen so as to be indicative of the completion of defrosting Since the 'thermostat I4 is placed at the coolest part cooling unit, except when unfrozen liquids are positioned therein, and is lordinarily' exposed to temperature of the air cooled v there until the switch is again 01' the the temperature of the frozen materials within the freezing chamber, a setting at a temperature somewhat below the actual freezing point is ordinarily preferable.

Assuming that the without frost, the thermostat I4 will be in the on position as shown in Figure 2, and the thermostat I3 alsol will be in the position shown in Figure 2. As the box is cooled to of its intended operating range, the thermostat I3 will contact with and move the finger I6 and tilt the switch I9 to its off position, thereby stopping the motor 2| and interrupting refrigeration. As the air in the box becomes warm the thermostatA I3 will move towards finger I5 and as the upper limit of the temperature range is reached the finger I5 will be moved until the switch I9 is tilted to its "on position, the motor 2I will then be startedand the refrigerating cycle repeated.

This temperature control by the thermostat I3 will continue repeatedly until frost has accum lated on the cooling surfaces to such an extent that the interior or freezing chamber at the `thermostat I4 is cooled below its normal low limit before the thermostat I3 re'aches its low limit, vwhereupon the'thermostat I4 will contact the nger I8 and move the switch 20 to its "off position.

With the circuit broken at the switch 20, the operation of the motor will not be restored if the upper limit of the normal temperature range is cooling unit is operating the lower limit reached in the box I0, but only when one of two or when unirozen liquids are placed in the freezy ing chamber so that their heat is transmitted to the thermostat I 4. and the latter is operated to close the switch 2li;

Assuming that the refrigerating device is one which attains the coldest temperature in the cooling unit, while the motor is operating, the switch I9 will always be on when the switch 20 is o since the opening of the switch I9 would cause a reversal of the temperature change, and consequently would prevent the opening of the switch 20. Consequently, if at any time during the defrosting period, any material which is to be frozen is put into the freezing chamber so as to raise the temperature of the thermostat I4, the motor circuit will be 'closed and freezing will begin immediately. So long as i'reezing is not required, however, the defrosting will continue until it is completed.

tact 21 which is to cooperate with the adjustablel contact 28 positioned on the ends of the adjustable screw 29. The screw 29 may be secured in any convenient support not shown and the contacts 21and 28 may be connected into the circuit as shown in Figure 2 or intoother circuits, e. g.,

` makes contact directly `'I0 circuit is open as described below and shown in the following iigures.

In the operation of this device, the coniining action of the periphery of the disk itself and of the ring serves to prevent a uniform movement of the contact 21 away from the contact 28, but may be designed substantially to hold the contact between them until sufllcient stress is aci cumulated by the difference in expansion between the two layers of metal disks to snap the disksto an opposite curvature. For purposes of illustration, the curvature ofthe disk is exaggerated in this figure of the drawings, and ordinarily the contacts 28 and 21 should be placed so that there is just enough curvature in the disk 26 to assure this snap action and prevent a continuous movement of the contacts, 'such as would be liable to draw an arc between them.

In Figure 4 another type of thermostat for the same purpose is shown. In this case a spiral bimetallic strip substantially the same as that shown at I3 and I4 in Figure 2 is used, but in this case insteadof the mercury switches I9 and 20, a direct contact 21a, and 28a is used and in order to prevent arcing by a slow separation of thev contact pointsjthe spring detent 30 is used with a cam ridge such that the extension 3l on the thermostat will hold the contact 21a against movement until enough force has been accumulated to snap the extension 3I over the ridge on the spring 30. An adjusting screw 32 may be provided to regulate the tension on the spring 30.

`In Figure' 5 I have shown another embodiment of my invention which is more especially adapted for use with refrigerating devices which have a carry over -such that thecoldest temperature in the box may occur after the refrigerating motor has been stopped. l l i In principle this device is the same as that of Figure 2, but electrical relays-and circuits are used instead of mechanical features.

In this case the thermostats I3 and I4 may be substantially the same as those illustrated in Figure 2 except that in this case they serve as conducting members making contact as will be hereinater described, and the thermostat I3 also carries a contact 35 'insulated from the thermostat itself.

The circuit connecting the motor 2I to the power line 22 is in this case controlled by the relays I9a and 26a operating in series in the same way that the switches I9 and 20 operated in the embodiment illustrated in Figure 2. These relays in turn are controlledy from the thermostats I3 and I4. l

The relay circuits are energized from the linej or from any other suitable current source through the connections 36 and 31, the former in this instance having a resistance or other suitable means for decreasing the voltage and limiting the cur` rent flow in the control circuit. u.

The relay I9a is energized through a second resistance 33 which serves to isolate its circuit from that of the relay 20a so that it may be shorted, to drop its armature, without shortlng vthe relay 20a.-

The armature of the relay I9a is connected to the return connection 31 as shown at 439 and to a self-energizing shunt 40 by which the relay is held up even after theat the thermostat contact 35. The armature I9aalso carries contacts 4l and 42 in sulated from the armature. I'he lower contact 42 .closes vthe motor circuit, as already described,

permit contact with 45, and if the while the motor the short-circuit 4s to the thermostat I3 when the relay is energized.

The relay circuit is completed through the connections 44 and 45, the contact 35, the thermostat I4 and the return connection 31. The short-circuit 43 islcompleted through the thermostat I3, the connection 46 and the return connection 31.

The relay 20a, like the relay I9a carries two insulated contacts 48 an 49, is itself connected through the connection 39 to the return connection 31 and makes contact directly with the selfenergizing or locking connection 50.

The lower contact .49, like the corresponding contact 42 of the relay |90., controls the circuit of the motor 2I while the upper contact 48, like the corresponding contact 4I, of the relay I9a., controls the short-circuit connection 5I by which both relays are shorted through the thermostat I4 and the return connection 31.

yThe circuit of the relay 20a is completed through the connection'52, the thermostat I4 and the return connection 31. The contacts of the connection at the relays I3 and I4 respectively may be made adjustable and in particular, the adjustment of the contact at the thermostat I4 may serve as the cold control.

The contact of 45 with the should, also, be resiliently mounted so that, upon further cooling of the thermostat, it can yield to the connection 52.

In the operation of this device, assuming that the refrigerator is operating normally without frost on the cooling unit, the armatures of both relays will be dropped and the motor circuit closed through the contacts 42 and 49. When the normal low limit is reached in the box Ill at the thermostat I3, the contact 35 will close the .circuit of the relay I9a between the connections 44 and desired freezing temperature has the cooling chamber, this circuit I4 and been reached in will be completed through the thermostat the return connection 31. Unless there is unfrozen chamber this circuit it is closed at I3 and the normal control 'therefore will 4be by the thermostat I3.

When its circuit is thus completed the relay I9a is energized and the motor' circuit broken at 42. Refrigeration is therefore'termnated unliquid in the freezing til the high limit temperature is reached at either thermostat. Assuming that the thermostat I3 is the first to reach its high limit, it will contact with the connection 43 and short-circuit the relay I9a dropping its-armature and closing the motor circuit at 42. While the thermostat I3 is moving between the contacts'44-45 and 43, that is to say, is between its two limits, the relay I9a is energized through the locking shunt 40, the armature I9a and the connection 39.

So long as the cooling unit remains free from frost and no warm liquids are put intov the freezing chamber, the operation of the device will continue under the control of the thermostat I3, substantially as described, with intermittent operation of the motor as required. If, however, is off, i. e., while the relay I9a liquid should be put into the for freezing, the thermostat is energized, a freezing' chamber thermostat I4 will `be closed at I4 before I4 would make contact with the connection 5I and thereby would short the entire circuit from the resistance 36 to the return connection 31, thus dropping both the relays I9a and 20a, and immediately starting the motor 2I. The operation of the motor wouldthen continuev only until the liquid thus placed in the freezing chamber was frozen sumciently so that the thermostat I4 was moved from the connection 5I to the connection 45, (assuming, of course, that the boxalso at that time had been cooled to such an extent that 5 the contact 35'had closed the connection -44 to the conn vtion 45).- If the box should not have been coo ed to the temperature at which the contact/35 closes the circuit between 44 and 45, refrigeration would, of course, continue until this occurred. f g

As the frost gradually accumulates on the surface of the cooling unit, the temperature within the freezing chamber when the low limit of temperature is reached in the box, will become progressively lower in each successive cycle until a defrosting limit is reached substantially below that at which contact-is made with the connection 45 at the thermostat I4. At this point, the thermostat I4 contacts the connection 52 through which the relay 20a is energized. The motor circuit is opened thereby at 49; and the relay 20a is locked up through the connection 50. 'I'hus a defrosting period is begun. In Figures 6 to 8, I have illustrated another embodiment of my invention in which the inner and outer-thermostats I4 and I3 respectively are mechamcally'instead of electrically inter- 1 connected by means of the rock shaft 55 and the alms 56 and 51. One of the thermtats by engaging the arm 56 shifts the contacts on the arm 51 relative to the other. With this arrangement, either one of the thermostats is reversed with respect to the otherl or they are made with the bi-metallic strips reversed, in opposite directions with a. given change in temperature. l

A spring detent 6,0 holds the rock-shaft in either position.

'I'he control lcircuit may be substantially the same as that shown for the relay I4 in Figure 9, except that there need be no break in the motor' circuit at 35a. If a snap switch, e. g., such as those shown in Figures 3 and 4, is used, a single contact 58 may be used to complete the motor circuit directly omitting the second contact 59 and the relay circuit. y

Referring particularly to Figures 7 and 8, thev normal control of refrigeration will be by the thermostat I3 making contact at 58 and 59 respectively whenthe upper and lower limits of normal operation are attained in the box I0.

When the temperature within thev freezing chamber reaches a low limit indicative of excessive frost, the thermostat I4 willmove the arm 56 and thereby shift the contacts 58 and 59 so that the motor will not be turned on when the normal upper limit is reached. 'I'he spring 5,0 holds the arm 56 in this position to which it has been moved by the thermostat I4, andthus thedefrosting period, initiated when the arm 56 is moved to the left, will be completed only when the temperature in the freezing chambers has risen to a point indicative of completion oi' defrosting or insertion of` a material to be frozen at which time the thermostat I4 will move the arm 56 back to the normal position. Thereafter the normal refrlgerating cycle Will again control.

In the embodiment shown in Figure 9 the relay I9a associ-ated witlnthe thermostat I3 has been replaced by a snap switch similar to that illustrated in Figure 4 while a deirosti'ng relay a is still provided.

The circuit of the motor 2l in this case is '.75 controlled through the contact member 49l on the` 52. During the dei'rosting so that they move i thermostatv I 4a, the

anonce relay 20a and the contact membera on the thermostat Ila.

'Ihe circuit of the relay the thermostat I3 when at its defrostlng limit by the connection 52a and is short-circuited at its high temperature limit through the connection 5I, the amature of the relay and the connection period the relayv 20a is locked up by the self-energizing connection 50a-39a connected through the insulated contact 48 on the armatureof the relay 20a.

, In the operation of this device the normal control is by the snap thermostat switch I 3a controlled by the spring detent 30, but once the low temperature limit indicative of frost insulation.

is reached within the freezing chamber, the motomcircuit is openedat the relay 20a 'and a defrosting period is initiated which continues until the high temperature limit indicative of complete defrosting or insertion of a material to be frozen is reached.

With this device the insertion of material to be frozen does not invariably start the refrigerating device, as it does in the embodiment of Figure 5, but as in all present commercial refrigerators, freezing must await the operation of the outside control I3a. Il. immediate starting is desired, this can easily be attained by use of a resistance heater associated with the thermostat I 3.a and forming a partlof the connection 5I, so that when the upper limit is reached in the freezing chamber the operation of the thermostat Ita will be artiilcially stimulated.

" In all of the examples illustrated and described so far, theA accumulation and removal of vfrost is 20a is closed through.A

lao

determinedV by a direct measurement of the transfer capacity of the cooling surfaces under given cooling conditions by means oi thermostats placed within and without. 'Ihe outer thermostat represents the usual temperature control and although shown as a speciilc type and in a specific circuit relationship, it is to be understood that any thermostatic controls of the refrigeration such vas have been commonly used heretofore can serve as this outer thermostat, the inner thermostat then serving to render the refrigeration device .inoperative after the low temperature limit has been reached within the freezing chamber and until the high vtemperature limit has been reached.

It is also possible to use the inner Vcontrol as the sole thermostatwcontrol of the refrigeration. I have illustrated for example in Figures 10 to l2. In this case the thermostat I4 is adapted to close the motor circuit at a temperature within the freezing chamber which under normal operating conditions is indicative of the desired temperature in the box I0. Once the motor 2| is started it rotates the commutator III shown in Figures l1 and 12 so that by the time the tem perature within the freezing chamber is sufciently reduced by the operation of the refrigerating device to separate the .contact -of the brushes 'II and 12 are on a conducting portion of the commutator I0 and the motor circuit therefore remainsV closed throughv this parallel connection I2-I0-`II.

The commutator l'Nils geared to the motor atv such ratio that one revolution will normally sufilce for lowering thel temperature within the box from the normal high-limit to the normal low limit when there is no excessive frost accumulation, and will sufilce to lower the temperature to the defrosting limit when mor mum permitted frost is on' the cooling surface.l

than the maxithis device, the normal refrigeration is turned on by the closing of the contact upon movement of the thermostat I4a to the right and is turned oif, after the contacts of the thermostat |4a have beenseparated by the completion of a revolution of the commutator 10 so as to bring its insulating portion 14 under one of the brushes. .Normally the extension 16 oscillatesin front of the ridge on the detent 30. If, however, the cooling surfaces have been so far insulated by frost as to cause an excessive decrease intemperature during the revolution of the commutator 10, the extension 16 on the thermostat |4a will have 'passed over the cam ridge on the spring detent 38 with the result that the thermostat l4a will be held out of contact with the connection" until a high temperature has been reached corresponding to completion of ldefrosting or insertion of material to be frozen.

The commutator 1l! driven by the motor 2| is in this case representative of a timevdelay device which assures the operation of the refrig- In the operation of erating device for a period after it is started which is sufficient to produce the desired reduction in temperature under normal operatingconditions without frost and to produce an excessive reduction of temperature sufcient to shift the thermostat to its defrosting condition when a given amount of frost has accumulated. Figure 12 illustrates a modification of the same type of control except that instead of a commutator 18 a cam 10a is provided which operates the tilting switch 18 to close the circuit between the connections 'Ila and 12a.

The device illustrated in Figures 10 to 12 is most closely related to those specic embodiments of my broad invention which were disclosed in my prior application Serial No. 618,220, the thermostat i4a in this case being responsive to the use of the refrigerator instead of the door operated device, and the motor drive commutator replacing the ow or clockwork delay mechanism.

As will be readily understood, the thermostat may be replaced by other delay initiating means,

- tion of this device, the thermostat normally oper-` e. g., as those disclosed in my said prior application or the delay means may be replaced by others, e. g., such flow or clockwork devices as are disclosed in my said prior application.

In Figures 13 and 14 I have illustrated'another embodiment of my invention in which a single thermostat within ,the .freezing chamber is utilized. The same assumptions as to the temperature within the box i0 are lmade as in the case illustrated-in Figures 18 and 12.

In this case a mercury switch 80 is mounted on a carriage pivoted at 8l and having projections 82, 83 and 84 adapted yto contact with the end 85 of a thermostat which is shown only in cross section at 85. An S- guide 86 holds'the thermostat end 85 in or away from the path of the projections 82- and 83. In the normal operaates within the range between the'projections 82 and 83, moving rst one and then the other to tilt the switch to on and off positions respectively. If, however, the temperature within the freezing chamber should become sumciently cold to permit the end 85 of the thermostat to slip over the lower end of the S-guide 86, then the thermostat would have to be warmed t'o a temperature sufliciently high to allow it to pass over the upper end of the end guide 86 and push the projection 84-to the on refrigerating device could again operate. The temperature at whichit may thus pass over the Y own delay device.

' of the refrigerating skilled in lthe art will be understood, however,

position before the upper end of the S-guide 88 and move the proiection 84 is ordinarily chosen as that which is indicative of completion of'defrosting or insertion of materials to be frozen. Since the thermo'- stat end 84 is retarded and deflected by the curved end of the S-guide, the thermostat tends to snap the projection 84 .on the switch carriage immediately to the on position as soon as it is released from the guide 86. Upon further cooling from this temperature due to the renewed operation of the refrigerating device, the end 85 passes along the left hand side of the S-guide and again contacts with the projections normal temperature range.

This control may be used in place of the thermostat |4a shown in Figure 10 or with any other suitable delay device, but is particularly adapted for use with a refrigerating device which has a substantial carry-over so as to serve as its For example, a device which accumulates a substantial' supply of condensed refrigerant during its operating period which continues to evaporate after the vvoperating period and thereby to cool still further the interior of the freezing chamber after the refrigerating circuit is opened. It is particularly satisfactory where it is combined with a thermostatic valve responsive to temperature within the box I8 which controls the admission of refrigerant to the cooling unit so that up tothe extent of the refrigerant supply accumulated during operation device, the refrigeration may continue after the opening of the switch 88 so long as the temperature within the box l0 is above the normal low limit.

82 and 83 to maintain the` From the above description and accompanying drawings, it will have become apparent to those bodied in a wide variety of apparatus of which the specific examples given are only a few. For purposes of illustration I have used the simpler case in which a motor is controlled directly as in the case of domestic electric refrigerators. It that the device which I have indicated diagrammatically at 2| and referred to as a motor may be any type of refrigeration control, as for example, an electrically controlled valve or a relay or any other that my invention may be em,-

type of electric referigerating device, whether operated by a motor or not, and any other type of electric control for a refrigerating device, whether the latter is operated by electricity or not.

-Ina broad aspect the invention contemplates the combination of means responsive to frost accumulation with means respo vsive to use of the freezing chamber, the latter` eing the domi-l nant control so that although defrosting periods will be automatically initiated when the accumulation of frost demands,` nevertheless, the defrosting will always be put o whenever the freezing chamber is in use. As above disclosed I havel and economical means for combination by using a therfreezing chamber to deterprovideda simple accomplishing this 'mostat within the mine the use of the chamber b y response to temunfrozen materials inserted therein and to determine or assist in determining the accumulation and removal of transfer through' the wall of the chamber, reliance being had upon the fact that with accumulation of frost the outer wall of the cooling unit will be insulated so that the refrigerant therein will produce a greater cooling effect upon the interior of the freezing chamber.- This is espeperatures of frost by the heat to the cooling unit a limited flow of refrigerant less than wo refrigerating device may be initiated uld reduce `the entire cooling unit to` its yevaporating temperature,.or in which the pressure within the evaporator (and consequently the temperature of evaporation) is reduced by the refrigerationg device when therate of evaporation is reduced.- Accordingly, I prefer to use of these types.

Although I have referred in the above specifically to the shutting off of refrigeration during the defrosting periods, it will be understood by those skilled in the art that a defrosting cycle instead which is designed to maintain a higher than normal temperature, but below some given limit so that if the temperature in the box should exceed that limit, refrigeration mightbe resumed for a short period after which defrosting would continue. 'I'hese and numerous other changes are within the scope of my present invention.

In the laccompanying claims-I have used the term "power refrigeration" and variants thereof chilling unit positioned -said receptacle of material 'to be Afrozen and.

to refer-to refrigerators in which cooling is eiected by conversion of energy whether mechanical,

electrical, thermal crchemical, etc., rather than by simple absorption of heat by melting of ice.

What I claim is:

1.'The combination of arefrigerator including a boxand av power refrigerating device having a within the box to cool the atmosphere thereof ltherein and said chilling unit having a receptacle .within which a freezing temperature is to be maintained, with a control for said refrigerating device including defrosting means adapted to render said device temporarily inoperative while frost is melted from the chilling unit, and means responsive to temperature within said receptacle to prevent interruption of refrigeration by the defrosting means while the temperature within said receptacle is above a predetermined temperature limit,l said temperature responsive means being in more intimate heat-exchange relation to the interior of said receptacle'than to the refrigerant. l 2. The combination of a refrigerator including a box and a power refrigerating device having a chilling unit positioned within the box to cool the atmosphere thereof and said chilling unit having a receptacle within which a freezing temperature is to be maintained, with a control for device comprising defrostingsaid refrigerating means adapted to render said device temporarily inoperative while frost is melted from the chilling unit, and means responsive to the placing in adapted to set the refrigerating device for operation to freeze liquids in said receptacle and adapted to render said defrosting means ineffective to interrupt refrigeration while it is thus set for freezing.

3. A refrigerator, including a box and a power refrigerating device having a chilling u nit positioned within the box to cool the atmosphere thereof and having a refrigerant therein, and said chilling unit having a receptacle within which a freezing temperature is to be maintained, and

defrosting control' means adaptedto interruptl operation .of the refrigerating device to effect defrosting ofthe chilling unit, which is characterized by temperature-responsive means in more intimate heat-exchange relation to the inside of said receptacle than to the refrigerant and adapted, regardless of means, to preclude Ithe interruption of operation and having a refrigerant the defrosting control,

of the refrigerating device when. but only when, the temperature within said receptacle is above a predetermined temperature limit.

4. In a control device for a refrigerator having a heat absorbing unit with a refrigerant therein anda receptacle in' said heat absorbingwY unit 'adapted for freezing liquids, the combination therewithoi' means responsive to temperatures created by said heat absorbing unit and adapted normally to regulate the iiow of refrigerant within the heat absorbing unit to maintain said temperatures .within alimited range, means for initiating a defrosting cycle, and means responsive tothe temperature within said receptacle, and in more intimate heat-exchange relation to the inside of said receptacle than to the refrigerant, adapted to terminate the defrosting cycle` when the temperature within said receptacle is as y high as a predetermined high temperature limit near the freezing point. 1 i

5. 'I'he combination as declined in claim 4 in which the means for initiating the defrosting cycle is a temperaturevresponsive device responsive toa predetermined extraordinarily low temperature in the receptacle.

6. The combination as deflned in claim 4 inwhich'the means for normal regulation, the means for terminating the defrosting cycle all include a common temperaturev responsive device responsive to temperature within said receptacle. 'I

7. In a refrigerator having a power refrigerating device with a heat absorbing unit, an automatic control device comprising circuit control means responsive to temperatures within said unit and adapted in response to a predetermined high temperature limit therein to initiate operation of the power refrigerating device, means to delay termination of such operation for a substantial` period after initiating, and -means adapted at a predetermined low temperature within said unit which is indicative -o'f frosting to prevent subsequent initiation of operation of the refrigerating device until a predetermined high temperature limit is reached indicative of completion of defrosting `o r the presence of a warm material requiring cooling. .8. The'combination4 as defined in claim 7 in which the power refrigeration device comprises an electric motor,v the means for determining the period of operation is a switch in a circuit adapted to energize the motor and means operated by said motor to close said switch upon its initial operation and to open it after a predetermined operation.

9. In a control for a motor driven refrigerating device, thermostatic means adapted to close the motor circuit at a predetermined high temperature and a switch closed by initial operation of the motor to maintain its circuit energized for a substantial period of operation and opened after a predetermined peration, and defrosting means adapted to open' t e motor circuit for a' defrosting cycle only after said predetermined operation.

l0. The combination of a refrigerator having initiatingpadefrosting cycle and means for an artificial refrigerating device comprising a cooling unit, a thermostat within the cooling unit, a second thermostat outside the cooling unit in the space cooled thereby, means associated 'with said thermostats adapted normally to initiperature of each has reached a predetermined normal low limit, and to initiate a defrostinggcycle Ihas again reached its upper limit,

when the temperature of the inner thermostat reaches asub-normal low temperature limit before the outer thermostat has reached its normal low temperature limit.

11. The combination of a power refrigerating device controlled by an electrical circuit and having a cooling unit, a thermostat within the cooling unit, a second thermostat outside the cooling unit in the space cooled thereby and electrical switch means associated with each of said thermostats adapted to condition said circuit to initiate refrigeration when both thermostats have reached their predetermined upper limits and to interrupt refrigeration after either thermostat has reached its predetermined lower limit until it the limits of the inner thermostat being respectively above and below the temperatures normally reached within -the unit when the outer thermostat reaches its upper and lower limits and the upper limit being a temperature reached within the unit when its surface is at a temperature assuring the melting of frost therefrom.

12. The combination as defined in claim 11 in which the cooling unit is in the form of a cabinet having a compartment within it for reception of ice trays, the inner thermostat is in such close heat-exchange relation to said ice tray compartment and its high limit is such that refrigeration will continue so long as the trays in said compartment remain substantially above a freezing temperature.

13. The combination of a refrigerator having an artificial refrigerating device comprising a cooling unit with a control device comprising a thermostat within the cooling unit, a thermostat within the cooled space outside the cooling unit,

" a circuit controlling the refrigeration by said device and having contacts adapted to break the circuit at either of two ints, a relay adapted to close and open said circuit at one of said points, parallel connections in the energizing circuit of the relay, one open at the inner thermostat, but closed thereby when the latter reaches a sub-normal temperature indicative ofV frost accumulation and the other open at said relay' but closed thereby when it is energized, a shunt connection around said relay open at said inner thermostat vnamed shunt whereby the closing until the latter reaches a temperature indicative of completion of defrosting and closed thereby at such temperature, a second relay adapted to close and open said refrigeration controlling circuit at the other of said points, parallel connections in 5 the energizing circuit of said relay, one open at both thermostats but closed at each when its temperature reaches a normal low temperature limit, and the other open at said' relay but closed thereby when it is energized, a shunt connection 10 around said relay open at said outer thermostat until the latter reaches a normal high temperature limit and closed thereby at such temperature, and a resistance in the circuit through said lastnamed shunt circuit will release the secondnamed relay but not the first, whereas the closing of the first-named shunt circuit will release both relays, said relay connections being parallel but connected to a common source of electromotive 20 force.

14. The combination as deined in claim 4, in which the means for initiating defrosting comprises means operative in response to a predetermined extraordinarily low temperature in the reg5 ceptacle to render means for normal regulation inoperative to regulate the refrigerating device for further cooling until the means for terminating the defrosting cycle has been operated.

15. The combination of a refrigerator having 30 an artificial refrigerating device comprising a cooling unit, means responsive to temperature within the cooling unit, means -responsive to temperaturesloutside the cooling .unit in the space cooled thereby, means associated with said temperature responsive means adapted normally to initiate refrigeration when the temperature affecting either temperature responsive means reaches a predetermined high temperature limit respectively and to interrupt refrigeration when the temperature affecting the rst named temperature responsive means reaches a predetermined extraordinarily low temperature limit before the temperature aifecting the second named temperature responsive means has reached a prea determined normal low temperature limit.

TRU'MAN S. SAFFORD.

of the last- 15 p 

